Everybody sneezes. Some sneezes are barely perceptible, others are loud and distinct, and still others come in multiples. Why do we sneeze? What’s happening when we sneeze?

Some liken a sneeze to a reboot of the system; a reset of the nasal environment. Sensory receptors in the nose are activated by mucous, germs, dust, pollen, animal dander, or pollutants. The activated receptors then send signals to the brain stem. The resulting sneeze expels mucous along with the irritants, and this reflex protects us from the particles that might otherwise enter our lungs. It clears our nasal passages so that we can keep on breathing. It happens when we’re sick, allergic, or even anxious. The bottom line is that sneezing is a part of our immune system, and helps to keep our body safe by clearing away bacteria, viruses, and more.

Are sneezes controllable? Certainly there is some degree of conscious control; just compare your public sneeze to your private sneeze. At the beginning of the sneeze, when the nose’s sensory receptors first become irritated, it is often possible to stifle it by pinching the nose and shutting the mouth. The next part of the sneeze involves inhaling deeply, and an involuntary blink (perhaps in order to protect our eyes?) and exhaling explosively. At that point, it’s too late to stop, but not too late to shield others. Saliva and whatever accompanies it is shot out at a speed of 30 to 40 mph or more. Due to the force involved, and the very small size of the particles, they can be hurled 5-20 feet away, or even farther. It’s no surprise that a sneeze is an effective way to send germs into a large area, and to spread infectious disease. That is why we are taught to sneeze into a tissue or into an elbow, and why we are reminded to wash our hands with soap and water (or an alcohol-based hand sanitizer) after sneezing and throughout the day.

Sneezing styles vary. The strength, sound, and volume of a sneeze depend on the strength of the abdominal muscles, the lung volume, and the size of the windpipe or trachea. The contents of the sneeze might be mostly expelled through the mouth, or might mostly come through the nose.

Injuries from sneezing do occur. The most common is muscle strain. Rarely, a violent sneeze has lead to stroke, miscarriage, car accident, broken blood vessels in the eyes, retinal detachment, and fainting. There are rare reports of hearing loss and vertigo as a result of a ruptured eardrum – likely caused by stifling the sneeze.

Some people sneeze multiple times. Perhaps those with chronic sinus disease or allergies require more sneezes to completely clear the nasal passages. In a few extreme cases, a teenage boy sneezed three to six times a minute for more than a month, and Guinness World Records lists a 12-year-old girl who sneezed about a million times over a year and finally stopped after more than two years.

One unusual sneezing trigger, affecting up to 35% of us, is looking at a bright light. This trigger seems to run in families. Perhaps it’s a result of a crossover of nerve signals, such that the nerve stimulated when the eyes see a bright light also stimulates the nerve responsible for the sneeze reflex. Similarly, plucking eyebrows may trigger that nerve and lead to a sneeze.

Working out may lead to sneezing; it certainly does for me. During a long hard run, I breathe large volumes of air (including allergens) and dry out my nasal passages. This leads to the creation of mucous, which leads to sneezes.

In some cultures, sneezing is a sign of good luck - which becomes bad luck if two people sneeze at the same time. Other cultures hold that a sneeze means that someone is talking about you behind your back. Saying “God bless you” may stem from the belief that with a sneeze, the soul (which presumably resides in the head) exits the body, and that by saying this, you are protecting the person who sneezes.

Your next sneeze is inevitable, so God bless you all!

Dr. Alan Frischer is former chief of staff and former chief of medicine at Downey Regional Medical Center. Write to him in care of this newspaper at 8301 E. Florence Ave., Suite 100, Downey, CA 90240.